1. Field of the Invention
The present invention relates to a method for enhancing a perceptibility of an image under a dim backlight condition, and more particularly, to a method for enhancing the perceptibility of the image by boosting a background luminance layer of the image.
2. Description of the Prior Art
Multimedia devices, particularly portable devices, are designed to be used anywhere and anytime. To prolong the battery life of the portable devices, various techniques are utilized for saving the LCD (Liquid Crystal Displayer) power of the portable devices since the backlight of the LCD dominates the power consumption of the portable devices. However, as known by those skilled in this art, the image viewing quality is strongly related to the intensity of LCD backlight. The dimmer the backlight, the worse the image quality is. Therefore, maintaining image quality under various lighting conditions is critical.
Relevant techniques can be found in the image enhancement and tone mapping fields. The conventional methods are mainly designed to maintain a human vision system (HVS) response estimated by a specific HVS model exploited in the method. There are many choices of such models, ranging from the mean square difference to complex appearance models. Among these models, classical contrast and perceptual contrast are the most exploited ones due to the fact that contrast is the most important factor that affects overall image quality. Classical contrast is defined base on the signal processing knowledge, such as Michelson contrast, Weber fraction, logarithmic ration, and the signal to noise ratio. On the other hand, perceptual contrast, which is different from classical ones, exploits the psychological properties of HVS to estimate the HVS response. Most perceptual contrasts are designed based on a transducer function derived from just noticeable difference (JND) theory. The transducer function transfers the image signal from the original spatial domain to a domain which can better represents the response of the HVS. The perceptual contrasts are then defined in the domain with the definition mimic to the classical ones. To take both the local and global contrast into consideration, the conventional techniques are often applied in a multi-scale sense, where larger scales are corresponding to contrast of a border region. Furthermore, different kinds of sub-band architectures are developed to help the decomposition of the multi-scale techniques.
Though the conventional methods have good results for common viewing scenario (i.e., 50% or more LCD backlight), they do not work well for dim backlight scenario as low as 10% LCD backlight. The main reason is that the HVS has different characteristic between these scenarios and the HVS response estimators used in the conventional methods are no longer accurate for the dim backlight scenario.
Therefore, preserving the perceptibility of the original perceptible regions becomes an important issue for image enhancement under dim backlight.